Accumulating-type powered roller conveyors are widely used in various manufacturing and transfer operations so as to permit goods to be transported to and between various locations, with the goods being handled on a "first in-first out" basis. One conventional type of such conveyor as utilized with small or lightweight goods (i.e., less than 50 pounds) permits the goods to accumulate one after the other at the output end of the conveyor, with the accumulated goods or articles automatically advancing to the discharge end when one or more articles are removed. The accumulated articles abut against one another and slip on the continuously driven conveyor rolls. This type of conveyor normally performs quite satisfactorily when dealing with articles of light weight since the driving force imposed on each article is hence of small magnitude, so that the line pressure which exists between adjacent articles and which accumulates along the row of accumulated articles thus remains rather small.
However, when dealing with heavy articles, particularly articles in excess of 500 or more pounds, such as engine blocks, then the driving force applied to each article is of a much greater magnitude, and hence the accumulated line pressure which exists on and is exerted through the row of accumulated articles thus becomes of large magnitude. This is undesirable since it often results in an excessive force being imposed on the stop located at the end of the conveyor, and hence severely restricts the number of articles which can be accumulated within a single row. For this reason, most accumulating-type powered roller conveyors when designed for use with heavier articles have necessarily involved the well-known and extensively utilized concept of "zoning". Such a "zoned" conveyor is divided longitudinally into a plurality of zones each having a preselected number of drive rolls associated therewith, and a suitable retractable stop is located at the discharge end of each zone. A rather complex system of controls, involving switches and the like, is provided for interconnecting the various zones so that articles will be permitted to advance from one zone to the next only when the sensors indicate an opening in such zone. In this manner, the number of articles within each zone and hence the maximum accumulated line pressure, can be limited to tolerable levels. These zoned conveyors, however, are necessarily complex both structurally and operationally due to the switches and related control elements, thereby making the conveyor relatively expensive to construct and install, and also increasing the required maintenance.
The present invention accordingly relates to an improved powered roller conveyor which successfully handles and accumulates heavy articles while resulting in the development of extremely small line pressure per article during accumulation, whereby substantially large numbers of such heavy articles can be successfully accumulated without developing excessive line pressure or force. This thus enables the conveyor of the present invention to be successfully utilized in situations wherein more complex zone-type conveyors were previously required. The improved conveyor of this invention is also adaptable for zoning, but permits substantial simplification of the overall conveyor in contrast to prior systems in that it does not require special gear ratios or drives for creating a gap between the articles when an article is being advanced from one zone to the next.
The improved roller conveyor of this invention also successfully handles and accumulates extremely heavy articles while permitting continuous and positive (i.e., nonslip) driving of the conveyor drive rollers. This conveyor is thus usable in situations wherein intermittent driving of the rollers was previously required, which intermittent driving required more complex drive arrangements employing clutches, controls and the like.
In the improved conveyor of this invention, a plurality of conveyor rolls are formed as elongated sleeves and are freely rotatably supported on support shafts which are slightly undersized relative to the sleeves. While all of the support shafts can be rotatably driven, nevertheless the preferred conveyor of this invention drives only selected support shafts at preselected intervals longitudinally along the conveyor. The sleeves and support shafts are provided with a special coating on the opposed surfaces thereof so that friction between these surfaces is greatly minimized, whereby a minimal drive force is hence transmitted from the driving shafts to the sleeves, which minimal driving force is sufficient to effectively convey the articles along the conveyor but which results in only minimal pressure on the articles and between the articles when they are stopped for accumulation purposes. Substantial numbers of heavy articles can thus be successfully accumulated while resulting in minimal accumulated line pressure.
While several accumulating-type powered roller conveyors are previously known which employ sleeves or wheels rotatably supported on driving shafts, nevertheless all of these known conveyors have failed to significantly minimize the line pressure on the accumulated articles, and hence have been incapable of accumulating heavy articles. For example, U.S. Pat. No. 3,337,023, issued to Kohl et al, discloses a plurality of axially aligned wheels of a special configuration which are individually rotatably supported on each drive shaft. Further, the wheels on adjacent drive shafts are in rubbing interfitting engagement with one another. This conveyor is undesirable since it is designed primarily for use in handling very light and delicate articles. Further, the use of a plurality of axially adjacent rollers or wheels on each drive shaft makes the overall structure extremely complex, unsuitable for use with heavy articles, and creates an alignment problem in that variable slippage can result in undesired sideward twisting or displacement of the articles.
U.S. Pat. No. 3,951,255, issued to Shuttleworth, also discloses a powered roller conveyor similar to that of Kohl et al, in that Shuttleworth also employs a plurality of axially adjacent rollers rotatably supported on each drive shaft, whereby this conveyor thus possesses substantially the same disadvantages, and is incapable of operating with heavy loads.
One further conveyor designed specifically for handling glass sheets is shown in U.S. Pat. No. 3,563,721, issued to Ritter. The Ritter conveyor provides an elongated sleeve which is freely rotatably supported in surrounding relationship on each drive shaft to permit slippage therebetween when the conveyed glass sheet is stopped. While Ritter was striving to minimize the driving friction between the conveyor sleeve and the drive shaft, and hence minimize the accumulation pressure, nevertheless Ritter utilizes a metal sleeve in surrounding relationship to a metal drive shaft, and hence the degree of friction between these members and the amount of driving force transmitted to the sleeve is still greater than desired. Since Ritter is conveying rather light articles, namely glass sheets, his conveyor can be successfully utilized for its intended purpose, although it would be unacceptable and, in fact, impractical for use with heavy articles since it would still result in excessive line p ressure and hence would greatly restrict the number of articles which could be accumulated. Further, any attempt to use the Ritter conveyor with heavy articles (500 pounds or more) would create extremely large friction forces on the metal sleeve, resulting in excessive heat and wear on the sleeves, whereby the sleeves would rapidly wear completely through the thin walls thereof.
Accordingly, it is an object of the present invention to provide an improved conveyor of a type similar to that illustrated in Ritter, but wherein the driving frictional forces between the drive shaft and the article support sleeve is greatly minimized in contrast to that possessed by the Ritter conveyor, so that the conveyor of this invention will permit the development of minimum line pressure between the accumulated articles, whereby heavy articles can be successfully conveyed and successfully accumulated in substantial quantities.
Another object is to provide an improved conveyor of this general type, wherein the opposed surfaces of the sleeve and drive shaft, which surfaces rollingly engage one another, are provided with a specialized coating which enables the friction to be greatly minimized to thereby effectively minimize the line pressure between accumulated articles.
A further object of this invention is to provide an improved conveyor, as aforesaid, which is greatly simplified both structurally and operationally, which can successfully convey and accumulate extremely heavy articles, which can successfully accumulate large numbers of such heavy articles without excessive line pressure being developed, and which permits the use of a nonzoned accumulating conveyor in many use situations which previously required the use of a multiple-zone powered conveyor.
Still another object is to provide an improved conveyor, as aforesaid, which permits continuous rotation of the drive rollers even though handling heavy loads, and which permits positive driving of these rollers.
Still a further object is to provide an improved conveyor, as aforesaid, which is also highly adaptable for use as a zoned conveyor, by permitting zoning to be achieved in a simplified manner and without the use of special drive devices and the like for creating a gap between articles when they are transferred between adjacent zones.